Brassica oleracea var. capitata (L), in the

Transcription

1 Pertanika 2(2), (1979) Field Efficacy of Several Selected Insecticides Against the Diamondback moth, Plutella xylostella (L) 1, on Cabbage, Brassica oleracea var. capitata (L), in the Lowland of Malaysia ROSLl B. MOHAMAD, YUSOF B. IBRAHIM, and CHONG WEI CHEONG 2 Department of Plant Protection, Faculty of Agriculture, Universiti Pertanian Malaysia Key words: Field efficiency; selected insecticides; Diamondback moth; cabbage j lowland Malaysia' RINGKASAN Keupayaan beberapa pilihan racun serangga yang didapati dipasaran telah diuji keatas ulat plutella, Plutella xylostella (L), pada kobis, Brassica oleracea val'. capitata (L), di kawasan tanah rendah (Ladang Universiti Pertanian Malaysia). Pada keseluruhannya, keputusan ujian ini menunjukkan acephate, methamidophos, dan bendiocarb semuanya pada 0.1% b.a., Bacillus thuringiensis pada Ig/I., dijlubel~zuron pada b.a., tiap-tiap satunya didalam 450 I. airfha. mengakibatkaj~ pengurangan Yal~g bererti (P ~ 0.05) keatas populasi larva. Racun-racun ini juga memberikan perlindungan yang sama pada daun-daun kobis, terutama daun-daun muda. Bersamaan dengan keputusan-keputusan awal, petak-petak kawal didapati memberi hasil pasaran yang agak rendah, lebih bererti (P ~ 0.05) jika dibanding dengan petak-petak yang lilendapat rawatan racun-racun seral1gga.. SUMMARY l!.1ficacy of several selected insecticides available in the market were tested against the Diamondback moth, Plutella xylostella (L), on cabbage, Brassica oleracea val'. capitata (L), in the lowland (University ofagriwlture Malaysiafarm). Ir~general, the results showed that acephate, methamidophos, and bendiocarb all at 0.1% a.i., Bacillus thuringiensis at Ig./I., dijlubenzuron at 0.007% a.i., each in 450 I. of water/ha. caused significant reduction (P~ 0.05) in larvalpopulation. These insecticides also provided equal protection against larval damage on young hearting leaves of cabbage. Consistently, the control plots gave sign~ficantly lower yield (P ~ 0.05) of marketable heads as compared to the insecticide treated plots. INTRODUCTION The diamondback moth, Plutella xylostella (L), is a serious pest of cruciferous crops (Ankersmit, 1953; Asano et 0,1, 1973; Beri, 1958; Calora et ai, 1968; Hardcourt, 1955; and Lee, 1969). The status of this pest in Malaysia has been studied since 1957 by Henderson, followed by Ho (1965), Ho and Ng (1969), Wan (1970), and Ho and Tan (1971). In this country more than twenty generations of the pest have been recorded in a year (Chuo, 1973) with an average duration of 10.8 day life cycle (Ho, 1965). The larvae of the insect feed on the abaxial surface of the leaf, and in extreme cases skeletonised the plant. Currently, insecticide spraying is the most popular control method adopted by vegetable 1 Lepidoptera: pyralidae 2 Harrisons and Crossfield (M) Sdn. Bhd., Kuala Lumpur, Malaysia. Key to authors' names: Mohamad, R.B., Ibrahim, Y.B. and Chong, W. C. 84 growers in Malaysia. A wide range of insecticides have been used, particularly in Cameron Highlands; however, the general view of the farmers indicates that the intensive use of these insecticides has resulted in several of them becoming no longer effective. This situation further confirms the reports by Henderson (1957) that certain strains of this insect have developed resistance to DDT and BHC. Works in other countries have also showed that strains of Plutella had developed resistance to several other insecticides (Ankersmit, 1951; Tjoa, 1959; and Lee, 1969). There are also reports of,field effectiveness of insecticides and microbial agents against the larvae of this moth (Ho, 1965; Chuo, 1973; Creighton and McFadden, 1975; Asano et ai, 1973; Ho and Ng, 1969; and Ho and Tan, 1971). These studies were, however, either conducted in the vegetable areas of Malaysian Highlands (Cameron Highlands), or in other countries. In

2 R. B. MOHAMAD, Y. B. IBRAHIM AND W. C. CHONG view of the increase in acreage, and the consequent higher production of lowland cabbage in Malaysia, a study on the efficacy of some of the latest insecticides available in the market against P. xylostella (L) on this crop is imperative. It is hoped that the results from this study will throw some light on the choice of insecticides for the control of the pest. MATERIALS AND METHODS The experiment was conducted at the farm of the University of Agriculture Malaysia, Serdang. A randomized complete block design with four replicates was employed. Brassica oleracea var. capitata (L) (K-K cross) was used as test plants. Cabbage seedlings were initially grown in an insect proof glass house for five weeks, after which they were transplanted in the field on raised beds (1m X 23m) at 0.75m apart. The beds were enriched with chicken manure at the rate of 15 tonnes/ha., two weeks before transplanting. There were 13 plants per experimental unit, separated by two guard rows, planted on a triangular pattern and spaced at 0.5m between plants. Top dressings of compound fertilizer (NPK 15:15:15) were applied at one week and four weeks after transplanting at a rate of 12g/ plant at each application. Chicken manure was again applied at the rate of 100g/plant two weeks after transplanting. Five insecticidal treatments and a control at the rate of of water/ha. were carried out for each replicate. The insecticides applied were: acephate (Orthene 75SP ) at 0.1 % a.i.; Bacillus thuringiensis Berliner var. Kurstaki (Thuricide HP 3.2% ) at Ig/I.; bendiocarb (Garvox ) at 0.1 % a.i.; diflubenzuron (Dimilin 25WP@) at 0.007% a.i.; and methamidophos (Monitor 600 ) at 0.1% a.i.. Water was u~ed. for the control. A total of six spray apphcatlons were made at weekly intervals, starting two weeks after transplanting, with Killaspray-air flow sprayer fitted with a hollow cone nozzle. Assessment was done by pre-spray (one day before each subsequent spray) counting of the larvae on every third plant of each treatment sampled systematically, totalling five plants per plot. Occurrence of leaf damage as a measure of effectiveness of the treatments was assessed weekly commencing at seven-week old plants. At this stage each cabbage plant had more than ten leaves. The formula by Chuo (1973) was used to compute the severity index for each treatment. RESULTS AND DISCUSSION Larval Count. Table 1 presents the total number of living larvae for samples recorded, at 1 week intervals before each spray was conducted. Significantly higher number of larvae was recorded in the control as compared to all the insecticidal treatments. No difference was, however, detected among the insecticides tested. Chuo (1973) and Kouskolekas and Harper (1973) also reported satisfactory control of the insect with methamidophos, acephate, and B. thuringiensis. Although a highly significant result was obtained between control and insecticidal treatments, this was perhaps not a true reflection of the effectiveness of the insecticide. This method of assessment (larval count) may only be applicable up to a certain stage of crop growth. Generally, there was a decline in the larval count after the fourth spray except for B. thuringiensis treatment where the number began to decline only after the fifth spray (Table 2). It was noted that control plots registered a lower larval count than the treated plots from the third spray onwards. This decline in the number of larvae could be explained by the fact that the plants in the control plots were severely damaged by then, and as such lacking in fresh leaf surfaces for oviposition. This result, therefore, revealed that prespray larval count is a poor indicator of insecticide efficacy since reduction of leaf surface due to larval feeding will also reduce oviposition activity and thus reduce the number of larvae. The general decline from the fourth count onwards was a phenomenon also discussed by Henderson (1957), Ho (1965) and Chuo (1973), that population of Plutella was known to decline when the cabbage reaches maturity. Table. 2 also showed a general trend of increase in the number of larvae in acephate, bendiocarb and methamidophos treatments on the fourth sampling date. This could perhaps be due to the inception of a new generation. However, the increase was not high enough to give an overall significant result among the insecticidal treatments. Foliage Protection. Results obtained from the calculation of foliage protection index indicate that all insecticidal treatments gave significant foliage protection against larval damage in comparison to the control (Table 3). Chuo (1973). and Kuoskolekas and Harper (1973) reported similar findings from field trials with methamidophos, acephate, and B. thuringiensis. Field tests have also indicated that bendiocarb was 85

3 EFFICACY OF SELECTED INSECTICIDES AGAINST DIAMONDBACK MOTH TABLE 1 Total number of living larvae P. xylostella recorded after 6 samples. UPM,1977 Treatments Number of living larvae I II III IV Mean Control a Acephate b Bendiocarb b B. thuringietlsis b Diflubenzuron b Methamidophos b Means fonowed by the same letter are not significantly different at 5% level of probability (DMRT). TABLE 2 Weekly prespray count of living P. xylostella larvae. UPM,1977 Total number of living larvae at each count Treatments August September 13th 20th 27th 3rd 10th 17th Total Control Acephate Bendiocarb B. thurillgiellsis Diflubenzuron Methamidophos TABLE 3 Foliage protection index and percent marketable heads after insecticidal treatments against P. xylostella. UPM,1977. Foliage Protection Index Marketable Heads Treatments Mean (%)1 % increase Mean (%)1 % increase above control above control Bendiocarb 78.7a a Acephate 82.9a a Methamidophos 81.7a a B. thuringietlsis 75.2a a 97.1 Diflubenzuron 77.5a a 90.8 Control 53.8b 0 4l.1b 0 lmeans in the same column fonowed by the same letter are not significantly different at 5% level of probability (Duncan's Multiple Range Test). 86

4 R. B. MOHAMAD, Y. B. IBRAHIM AND W. C. CHONG effective against numerous species of Lepidopterans that feed on foliage (Lemon, 1971). Diflubenzuron was reported by Granett and Dunbar (1975) to be very effective in protecting the foliage of apple trees against gypsy moths. In this study no significant difference was obtained among the different insecticidal treatments. Evidently, these insecticides gave an overall protection of cabbage leaves against the P. xylostella larvae. Marketable Heads. The percent marketable cabbage heads in all the insecticide treated plots was significantly higher than that of the control plots (Table 3). There was however no significant difference among the insecticidal treatments. This showed that the insecticides employed were equally effective in preventing damage to the head, but the fact that bendiocarb, methamidophos, and acephate produced considerably more plants with no holes on the heads suggest that they killed the larvae more rapidly than did B. thuringiensis or diflubenzuron. Chuo (1973) and Creighton and McFadden (1975) also obtained satisfactory heading with methamidophos, acephate and B. thuringiensis. Apparently, all the insecticides tested provided considerable protection against P. xylostella damage to the young hearting leaves. Yield Assessment. Table 4 indicates that there were significant differences in yield between the insecticide treated plots and the control. No significant difference in yield was detected among the insecticidal treatments, even though acephate, methamidophos, and B. thuringiensis registered considerablly higher yield. These results con- TABLE 4 Yield of marketable cabbage at harvest. UPM, 1977 Mean weight per Expected Treatments cabbage head yield _ (g)l (kgjha.)2 Acephate 733a Methamidophos 722a B. thuringiensis 712a Bendiocarb 626a Diflubenzuron 594a Control 300b lmeans followed by the same letter are not significantly different at 5% level of probability (Duncan's Multiple Range Test). 2The expected yield is based on experimental results estimated from 25,000 cabbage headsjha. firmed the reports that acephate, methamidophos, and B. thuringiensis were effective in protecting the cabbage from yield' loss thus promoting high er yields (Ro and Ng, 1969; Chuo, 1973; Creighton and McFadden, 1975). CONCLUSION The various assessments indicated that the efficacy of the insecticides for the control of P. xylostella was quite consistent. The cabbage heads for market appearance, in treated plots were visually larger and almost free from damage compared to those of the control plots. The plants in the control plots were so badly damaged that only limited marketable heads could be salvaged at harvest. It was observed that early protection of the cabbage plants against the diamondback moth was essential, especially during the hearting stage. Plants badly damaged at this stage recovered by producing multiple heads which were of no economic value. It is thus imperative to use effective insecticides with quick knockdown action during this period in order to ensure a good harvest of the crop. ACKNOWLEDGEMENT The authors wish to thank Universiti Pertanian Malaysia for providing the facilities, Rarrisons and Crosfield (M) Sdn. Bhd. for providing the chemicals, and Encik Abd. Ghani Ibrahim for reviewing the manuscript. REFERENCES ANKERSMIT, G. W. (1953): DDT-Resistance in Pilltella maclllipennis (Curt.) (Lep.) in Java. Bull. Entomol. Res. 44(3): (Abstract). ASANo, S, H. SAKAKIBARA,T. KITAGAKI, K. NAKAMURA and Y. MATSUSHITA (1973): Laboratory and field evaluation of the effectiveness of Bacillus thllringiensis products 'Thuricide on some Lepidopterous pests of crucifers. Jap. J. Appl. Entomol. and Zool. 17(2): 91-6 (Abstract). BERI, Y. P.(1958): Field. experiments on the cabbage pest control. Indian J. Entomol. 20(1): CALORA, F. B., GLASS, E. H., PESCADOR, M. L. and BARROGA, S. F. (1968): Granular soil systemic insecticide (Thimet and Cyolane) and phosdrin foliar spray against the diamondback moth, Pilltella maculipennis Curtis and other pests of cabbage. Philip. Entomol. 1(1): (Abstract). CHUO, S. K. (1973): A screening experiment to test the efficacy of four insecticides against diamondback moth, Plutella maculipennis Curtis and cabbage. web-worm, Hellllia undalis F. Singapore J. Pri. Ind. 1(2):

5 EFFICACY OF SELECTED INSECTICIDES AGAINST DIAMONDBACK MOTH CREIGHTON, C. S., and Mc FADDEN, T. L. (1975): Cabbage caterpillars: Efficacy of chlordimeform and Bacillus thuringiensis in spray mixtures and comparative efficacy of several chemical and B. thuringiensis formulations. J. Econ. Entomol. 68(1): GRANETT, J., and DUNBAR, D. M. (1975): TH 6040: Laboratory and field trials for control of gypsy moths. J. Econ. Entomol. 68(1): HENDERSON, J. (1957): Insecticidal control of the d amondback moth (Plutella maculipennis Curt.) on cabbages at Cameron Highlands. Malay. Agric. J. 40: HARDCOURT, D. G. (1955): Biology of the diamondback moth, Plutella maculipennis Curt. (Lep.: Plutellidae), in eastern Ontario. I. Distribution, economic history, synonymy and general descriptions. 37th Rep. Quebec. Soc. Prot. PI Ho, T. H. (1965): The life-history and control of the diamond-back moth in Malaya. Div. of Agric., Ministry of Agriculture and Co-operative Bull. No. 118, Kuala Lumpur, Malaysia. Ho, T. H. and NG, K. Y. (1969): Bacillus thuringiensis Berliner for the control of diamond-back moth in West Malaysia. Malay. Agric. J. 47: Ho, T. H. and TAN, S. (1971): The life h story and control of the d amond-back moth. Div. of Agric., Ministry of Agriculture and Co-operatives Tech. Leaflet No.5, Kuala Lumpur, Malaysia KOUSKOLEKAS, C. A. ~nd HARPER, J. D. (1973): Control of insect defoliators of collards in Alabama. J. Econ. Entomol. 66(5): LEE, H. S. (1969): Experiment on the control of diamond-back Moth and aphids on chinese cabbage. Pl. P, oct. Bull., Taiwan. 11(1): 43-5 (Abstract)- LEMON, R. W. (1971): 2,2-DiMethyl-1, 3-benzodioxol. 4-yl N-methylcarbamate, a new broad spectrum experimental insecticide. Chesterford Park Res. Sta., New Saffron Walden, Essex, U.K. pp (Abstract). TJOA, M. T. (1959): Results of tests of phosphorus insecticides against chlorinated insecticides resistant Plutella manulipennis in Lembang (West Java). Contr. Gen. Agric. Res. Sta., Bogor No. 155 (Abstract). WAN, M. T. K. (1970): The bionomics and control of the diamond-back moth, Plutella xylostella L. (P. maculipennis Curt.) (Lep.: Plutellidae) in Sarawak (Malaysian Borneo). Sarawak MuseumJ. 18: (Received 15 March 1979) 88